1. Technical Field
This disclosure relates to the fabrication of magnetic read/write heads that record at high data rates. More particularly, it relates to such a structure that incorporates a main writing pole that is responsive to high frequencies.
2. Description
For purposes of present high density magnetic recording, the recorded bits per inch (BPI) requires that the data rate at which writing occurs increases into the GHz (gigahertz) range. At this high frequency range, the bit error rate (BER) starts to increase along with the increasing frequency leading to a degradation of recording quality. In order to maintain recording quality by obtaining an adequate BER, it is critical that the frequency response of the writer be improved.
The frequency response of the writer is related to the speed with which the main writing pole can respond to the external current-driven magnetic field. Referring to FIG. 1a, there is shown a schematic illustration of a side cross-sectional view of a normal writer, in a plane through its main pole (20) center. The plane is perpendicular to its air-bearing surface (ABS) plane, which is shown as the dashed line (10). In the view shown, a magnetic medium (5) would be moving upward relative to the writer, so a leading shield (30) is below the tip (distal end) (25) of the main pole (20).
The main pole is supported from above by a top yoke (40), to which it is physically and magnetically coupled. Note that the term “top” will hereinafter refer to the horizontal trailing side of the main pole and the term “bottom” will refer to the horizontal leading side of the main pole. Note that the term “side” may often refer to a surface that is actually contiguous with another surface so that it forms an interface rather than an exposed or identifiable surface. Thus, when a top yoke is formed on a trailing side of a main pole the formation may be the result of a plating process so that the contiguous sides of the pole and yoke may actually form an interface. Nevertheless, when the term “side” is hereinafter referred to it will generally mean a surface or interface that can be envisioned as an identifiable horizontal plane.
A return pole (50) includes a trailing shield (60) (the term “trailing” here referring to the trailing side of the pole). Finally, the cross-sectional view also shows schematic cross-sections of two exemplary current carrying coils (80) (forming complete loops in a horizontal plane, the other half of the loop not being seen here) whose current activates the magnetic fields that are carried as flux by the main pole, emerging through the pole tip and creating magnetic transitions in the moving magnetic medium. The details of the closed flux loops will not be shown herein.
The overall structural shape of the writer determines the speed of the writing in the sense that the rate of change of current in the coils must be able to produce a correspondingly changing flux within the main pole/return pole circuit. This closed flux circuit fringes across the ABS at the tip (25) of the main pole and the writing speed depends on the rate at which the emergent flux can respond to the changing current.
The yoke (40), which here is a top yoke, is an additional structure of constant thickness t that can help the writing speed by the way in which it channels the flux to the main pole. The yoke is magnetically exchange coupled to the main pole and can be on top of the main pole (a top yoke), as it is here, or it can be beneath the main pole, forming a bottom yoke, or it can be formed in two segments, one on top and one on bottom. The yoke is usually recessed a certain amount from the ABS to reduce the disturbance of the shields on the write field. Disturbances by the shields can cause an undesired accidental data erasure (and corresponding high bit error rate (BER)) on tracks of the medium on which data has already been written. These tracks are usually immediately adjacent to the track currently being written on and the undesirable erasure effect is then denoted “adjacent track erasure,” (ATE); or there can be the creation of even wider zones of track erasure, called “wide area track erasures” (WATE). It is known in the art that reducing the distance between the yoke and the ABS can improve high frequency response of the writer, but it is also known that this will worsen the ATE/WATE and BER.
Referring now to FIG. 1b, there is shown the writer of FIG. 1a viewed from its ABS. Note that leading and trailing surfaces will appear as “edges” in this view. There is seen the return pole (50), the trailing shield (60) immediately below the return pole and contiguous with it, the emergent triangular (or, more generally, trapezoidal) face of the pole tip (25) of the main pole (the body of the main pole extends rearward, away from the ABS, and is not seen) and the leading shield (30) beneath the pole tip. When the disk drive is active, the movement of the magnetic medium is vertically upward.
Also seen in this ABS view but not seen (or not seen clearly) in the view of FIG. 1a, are a write gap layer (70) separating the pole tip from the leading edge of the trailing shield and symmetrically placed side gap layers (80) on either side of the pole tip. The leading shield (30) is shown beneath the pole tip.
As noted above, the conventional writer design of FIG. 1a and FIG. 1b is limited in its write speed by the ability of the magnetic pole to respond to high frequency variations in the coil current. Shortening the yoke-to-ABS distance can improve write speed, but at the expense of errors caused by overwriting adjacent tracks. Some approaches to addressing this problem can be found referenced below, but none of them provide the results of the present disclosure.
U.S. Patent Application 2010/0277832 (Bai et al) shows a tapered yoke on one or both sides of a main pole.
U.S. Pat. No. 7,841,068 (Chen et al) discloses in FIG. 7 a bottom yoke with a taper.
U.S. Pat. No. 8,107,191 (Im et al) shows a sub-yoke on top of a main pole at an angle.
U.S. Patent Application 2010/0321825 (Nazarov) shows a non-tapered top yoke.